Previously known from the Finnish patent 68390 is intensification of heat transfer in a double-decker glass bending furnace, where heat transfer is effected vertically between sections one on top of another by means of radiation and gravitational convection. The bottom of the mold carrier wagons is open enabling radiation and convection from the hot glass sheet on the bottom track section to the colder glass sheet on the top track section.
Further, a method to intensify heat transfer is known from patent FI-81331, where in comparison with the above solution, fans are installed to increase heat transfer from the bottom track section to the top track section.
Not even the last mentioned solution has turned out effective enough, because it works effectively only for a few seconds when the mold carrier wagons have reached a new position. There is then during this short moment enough difference of temperature for significant heat transfer. However, since the mold carrying wagons always stay for a time span of 1.5-3 minutes in a section before they are shifted over to the next section, the use of fans is quite useless.